(1) Field of the Invention
The present invention relates to electronic power supplies and more particularly to a circuit for protecting a battery powered, pulse controlled, constant current power supply from excessive power dissipation.
(2) Description of the Prior Art
Power supply protection devices are old and well known and are generally of the crowbar type. This type of circuit turns the power supply off when the amount of power being drawn exceeds a threshold level.
However, such crowbar protection circuits are incapable of protecting a power supply from failure due to an excessive duration of power dissipation as opposed to the amount of power dissipation. Duration of power dissipation problems are prevalent in pulse controlled power supplies. Such power supplies are generally designed to dissipate the power required for the duration of the control pulse, but if the control pulse should fail in the "power-on" mode, the continued full power dissipation will rapidly cause the power supply to fail. The usual solution to such duration of power dissipation problems is to design the power supply with expensive semi-conductor control devices and heat sinks so that the power supply can dissipate the power demanded without failure. But such a solution is expensive in terms of both components and space.
The Miller integrator, as described in Strauss, Wave Generations and Shaping, McGraw Hill, 1960, is similar to the Applicant's invention. However, the Miller integrator is a 3 terminal device and its output is the time integral of its input scaled by the circuit parameters. The Applicant's invention, in the first preferred embodiment, is a two terminal device whose output is not a function of its input and is determined solely by the circuit parameters. A second preferred embodiment was designed to depend on the input current yet still retain the two terminal structure.
Accordingly, it is the object of this invention to provide a new protection circuit for a battery powered, pulse controlled, constant current power supply that will turn the power supply off after a fixed period of time, requiring a minimum number of components and can be implemented as a two terminal device.